<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- * {
        border: 1px solid red;
        } -->
        <p>段落</p>
<b>加粗</b>
<span>无</span>
p {
    color: red;
    }
    <p>段落</p>
    #abc {
        font-size: 20px;
        }
        <p id="abc">段落</p>
        .abc {
            border: 1px solid red;
            }
            <b class="abc">加粗</b>
            <span class="abc">无</span>
            b.abc {
                border: 1px solid red;
                }
                <span class="abc edf">无</span>
                [href] {
                    color: orange;
                    }
                    [type="password"] {
                        border: 1px solid red;
                        }
                        [href^="http"] {
                            color: orange;
                            }
                            [href$=".com"] {
                                color: orange;
                                }
                                [href*="baidu"] {
                                    color: orange;
                                    }
                                    [class~="edf"] {
                                        font-size: 50px;
                                        }
                                        [lang|="en"] {
                                            color: red;
                                            p,b,i,span {
                                                color: red;
                                                }
                                                p b {
                                                    color: red;
                                                    }
                                                    ul > li {
                                                        border: 1px solid red;
                                                        }
                                                        <ul>
                                                        <li>我是儿子
                                                        <ol>
                                                        <li>我是孙子</li>
                                                        <li>我是孙子</li>
                                                        </ol>
                                                        </li>
                                                        <li>我是儿子</li>
                                                        <li>我是儿子</li>
                                                        </ul>
                                                        p + b {
                                                            color: red;
                                                            }
                                                            p ~ b {
                                                                color: red;
                                                                }
                                                                ::first-line {
                                                                    color: red;
                                                                    }
                                                                    ::first-letter {
                                                                        color: red;
                                                                        }
                                                                        a::before {
                                                                            content: '点击-';
                                                                            }
                                                                            a::before {
                                                                                content: '-请进';
                                                                                }
</body>
</html>